1. Field of the Invention
This invention relates to a sealant for geological formations and mine stoppings. The sealant is especially suitable as a coating for the stoppings and ribs and roofs of coal mines.
2. Description of the Prior Art
Stopping devices are used to control and direct the flow of air through underground passageways and to seal off portions of a mine. The stoppings are often installed in mines so as to direct air flow to the working face and prevent loss of air flow through cross cuts and entries which are not being worked. In ventilating the mine, fresh air is delivered under pressure to the working face and often must travel a considerable distance between the mine opening and the face of the mine. If the stoppings separating the crosscuts and entries are not sufficiently air-tight, the losses will be such as to effectively reduce the velocity of the air at the mine face. It is not uncommon for a mine to lose more than half of its induced air through leaking stoppings and doors. Consequently, the dust and gases in the area being worked by the miners will not be effectively removed to the outside of the mine.
Conventional stoppings consist of walls constructed of concrete blocks and cement, and are not very airtight. Sealants are employed to lessen stopping leaks. Current mine sealants generally are composed of various inorganic aggregates, including glass fibers, in conjunction with portland cement, and are characterized by a number of deficiencies. Because these sealants are applied at minimum thicknesses, are fragile and have limited adhesion to various substrates, such as trona ore, they crack readily whenever minor substrate movement occurs, resulting in spalling and hence loss of resistance to air leakage. Prior to application of these sealants, the pretreatment of mine ribs and roof areas is usually specified and/or required to enhance bonding and prevent dusting of the portland cement base. The recommended pretreatment is high pressure washing to remove rock dust and dirt. This is a labor-intensive and time-consuming operation requiring a water source, a significant amount of equipment and costly delays before sealant can be applied to pretreated areas. Further disadvantages of current sealants are their extremely short pot-life after mixing and the long time required after application for hardening (4-8 hours) and for the attainment of significant air and moisture resistant properties (in excess of 24 hours). Furthermore, the glass fiber often used is attacked by the high alkalinity of the hydrated portland cement, and therefore loses much of its tensile strength in just a few days. Other factors contributing to the high cost of using current sealants are the large dry storage areas required for raw material and equipment and the considerable manpower requirements throughout the operation.
It would be highly desirable if an improved sealant for application to mine stoppings and like formations could be found to overcome the above and other disadvantages of the prior art, and result in the provision of highly airtight constructions which can resist air infiltration for extended periods of time.